Heat treating furnace



3g of furnace is illustrated.

Patented Jan. 25, 1938 UNITEDA STATES l f :a,1o6,462I

`. HEAT TREATING FURNACE Le Roy Lindberg, Evanston, Ill., assigner to Lindberg Engineering Company, Chicago, lll., a corporation of Illinois Application october 12, 1935, serial No. 44,676

' 1 claim. (o1. 21e-a5) My present invention relates to a drawing or tempering furnace, and more particularly to an improved heating means which is applicable thereto. The features of construction herein disclosed are concerned with the use of certain heating elements, in the form of a resistance wire, in conjunctionl with a special mounting therefor.

r Such a heating means is particularly advantageous with a furnace having forced convection where a rapid circulation of air is maintained.-

In such an 'environment foreign particles tend to `lodge upon the heating elements, particularly upon the coils thereof at the turns around the supports or spoois. 'I'he accumulation of such particles will blanket the heat, thereby` tending to overheat the elements which, in consequence, are burned out faster. According to my invention I obviate all such' difficulty, and do this in a way which involves less expense and work in the construction of the heating means.

Referring to the accompanying drawing:

Fig. 1k is a central vertical section through a heat treating furnace having as one of its units a series of heating elements which are formed and 1 25 mounted in the manner which is peculiar to my invention; Y

Fig.' 2is a vertical section, on an enlarged scale, taken through the heating unit on line 2-2 of Fig. 1; and

30 Fig. 3 is an enlarged detail in section on line 3 of Fig. 2.

So far as concerns my present invention, the furnace may be any of the usual types-munie, well, etc. By way of example, a well known type As shown, it utilizes in its construction certain walls which dei-lne a well W open at the top but adapted to be closed by a lid L which may be moved to and from V.position with the aid of any suitable mechanism. With the 4c lid in place, as shown in Fig. 1, thewell is substantially sealed against the outside atmosphere.

The well constitutes the chamber in which the charge is treated. i

To one side of the well, and separated there- 45 from by a wall lil, is a heating chamber H. As

shown, this chamber extends vertically adjacent the well to one side thereof for substantially its entire length. The wall Il! terminates short of the chamber bottom so as to leave a communicating 50 opening H of ample size. Positioned withinthe heating chamber, adjacent this communicating opening and in connection therewith, is a housing I6 wherein may-be mounted a fan l1 of the blower type. The discharge opening of the housing faces 56 upwardly, and, as shown, is coextensive with'the be described. As shown, it comprises va frameentire cross sectional area of the heating chamber. As by means of a belt connection I8 the fan is driven from a motor M which may conveniently be mounted at a point exteriorly vof the furnace.

Mounted within the heating chamber, preferably by suspension, is a heating unit U which' desirably comprises a plurality of resistance coils adapted to be heated through connection with a source of electrical energy. This heating unit, as shown, comprises a head 20 below which the coils 10 are supported and above which is a cap 2| of enlarged size or diameter adapted to rest upon the furnace top. Electrical connections disposed on the upper side of the cap may be protected by a cage 22, as shown. A heating unit, so constructed 1,5 and located, is very accessible and may easily be removed, whether hot or cold, to be replaced by another similar unit, the entire operation requiring perhaps not more than two minutes time. When in place, as shown in Fig. 1, the interior of 20 the heating chamber is substantially sealed against the outside atmosphere.

At a point inthe upper region of the heating chamber, preferably just above the heating unittherein, is a passage 24 communicating with a manifold 25 which extends circumferentially around the well adjacentits top. By this arrangement heated air is supplied to the well directly above a charge that is contained therein.

The construction of the heating unit will now 3@ work made up of aseriesof interconnected horizontal and vertical bars and 3l respectively. Between the upper horizontal bars are supported a plurality of rods 32, and likewise between the lower bars other rods 33 are supported in opposing relation. Upon the bars are mounted a series of refractory spools in spaced relation. As shown, each spool may comprise two identical bushings 35 each formed adjacent one end with a circular ilange. With the bushings arranged oppositely in pairs, their flanges being to the outside, an annular groove 31 is provided between them. It will be noted that the width of this groove is determined by the distance between the facing sides of the flanges, its bottom being no wider than elsewhere. Each groove is accordingly open from top to bottom, with no constriction or obstruction of any kind. The several spool bushings, as already indicated, are maintained in spaced relation as by means of spacers 38. A like arrangement of spoolsis provided on each of the opposite rods. The several spools, so mounted in the framework, provide opposed supports for the heating elements whose construction will now be explained. 55

Each heating element is in the form of a helically coiled wire I0 extended between and carried within the .annular grooves of the spools. Throughout its region which lies within the spool grooves, each wire is formed into a single straight strand 4|, so as to lie in spaced relation to the vside walls of the groove whereby to deliver at such point a lesser degree of heat and in an environment where a free and unimpeded circulation of air is maintained.

In operation, a charge is received within the well W, being preferably contained within a pot P. With operation of the blower, air is circulated frorn the charge chamber through the heating chamber and thence through the manifold into the charge chamber again where it passes to lodge upon the heating elements, particularly at the portions thereof which are hottest and which oier the greatest impedance. It is found that this takes place largely around the spools where the heating coils are pbliged to make a turn. According to this invention the wire is straightened out wherever it passes around a spool. The groove in the spool wherein the wire islaid is of ample width, from top to bottom, to

allow a free circulation of air therein. The resuit is that a lesser degree of heat is delivered by the wire at this point adjacent the spool, and the air which circulates therethrough will readily carry away the heat thus generated so as not to blanket the heat in the way that is common at the present time with electrical heating units in heat treating furnaces. There is also a lesser tendency for foreign particles to lodge upon the heating elements at the points where they are supported by the spools, and in consequence the tendency for the wires to burn out is greatly reduced.

I claim:

In a heat treating furnace having a normally closed chamber in which is maintained a rapid air circulating system and an opening in one wall of said chamber, and means closing the opening in said wall and extending into such path of air circulation for heating the air in motion, said heating means comprising a caplike closure supported in said opening and having a framework on which is mounted spaced refractory supports, each having an annular groove, a heating element in the form of a helically coiled resistance wire extended between and carried within the annular grooves of the spaced supports, and the wire being formed in a single straight strand extending at substantially right angles tothe direction of the helixes of the coil throughout its regions which lie within the grooves of the supports and in spaced relation to the side walls thereof, whereby' less heat is delivered in the region of the supports and air circulation is unimpeded.

LE ROY A. LINDBERG. 

